1. Field of the Invention
The present invention relates to an ink jet head, and an ink jet apparatus provided with the ink jet head.
2. Related Background Art
An ink jet systems which conducts printing by forming ink droplets and projecting the droplets onto a recording medium like a paper sheet is advantageous, since the printing can be conducted with extremely low noise at a high printing speed, and color printing can easily be practiced with compactness of the apparatus owing to a smaller size of the printing head. Lately, a bubble jet system is noticed which ejects ink droplets by bubbling of an ink by heating element.
The ink jet head is prepared, for example, by forming a heating element, a driving circuit (e.g., a shift register), a wiring pattern on a silicon substrate by a conventional silicon process; die bonding the silicon substrate on an aluminum base plate onto which a printing substrate for contact with the main body of an apparatus has been preliminarily bonded; connecting the silicon substrate electrically with the printing substrate by wire bonding; bonding the base plate with a ceiling plate having grooves for an ink liquid chamber and an ink flow path formed by injection molding and an ink discharge opening formed by excimer laser with adjustment of the relative position of the ink discharge opening provided on the substrate and the heat-generating element provided on the ceiling plate; fixing the base plate with the ceiling plate by a spring; fixing further a member for supplying ink to the base plate by thermal caulking or a like method; and sealing the bonding interfaces with a sealant.
FIG. 1 illustrates schematically a disassembled ink jet cartridge which comprises an ink jet unit 13 having an ink jet head 12, an ink tank 14 and a cartridge body 1000. The ink jet cartridge is provided with an atmosphere communicating opening 1401 for communication between the inside of the ink jet cartridge and the outside air. A silicon substrate (heater board) 100 having a heating element formed thereon is bonded by die bonding onto a base plate 300 made of aluminum or the like. A print wiring substrate 200 is also bonded onto the base plate 300. The heater board 100 has a preliminarily formed heating element, a shift-register for driving, and a wiring pattern formed by a silicon process. On the wiring substrate 200, contact pads 201 for contact with the main body of the apparatus and wire bonding pads (not shown in the drawing) for contact with the silicon substrate are formed in a conventional wire bonding method.
A ceiling plate 1300 is fixed to the heater board with a spring 500. The ceiling plate 1300 has grooves for serving as an ink flow paths, an ink liquid chamber, and a nozzle (not shown in the drawing) formed thereon by injection molding, and has also an ink discharge opening 8 formed by laser processing. The ceiling plate 1300 is formed integrally with an ink-receiving opening 1500 for receiving ink supplied from the ink tank 14 and directing the ink to the ink liquid chamber, and also with an orifice plate 400 having a plurality of ejection outlets corresponding to the ink flow paths. The ceiling plate 1300 is bonded to the heater board with positional registration between the ink discharge opening and the heating element of the heater board, and fixed tightly by means of a spring 500.
Then an ink-supplying member 600, and an ink tank 14 are fixed onto the supporting member 300 by thermal caulking or the like method. The ink-supplying member 600 has an ink conduit 1600 communicating with an ink-supplying tube 2200 and cantilevered at the ink-supplying tube side. A sealing pin 602 is inserted at the fixed side of the ink conduit 1600 and the ink-supplying tube 2200. A filter 700 is disposed at the ink tank side end of the ink-supplying tube 2200. An inksupplying opening 1200 functions to supply ink from the ink tank 14 to the ink jet unit 13.
The gaps between these members are sealed with a sealant to prevent leakage of ink. The sealant is required to fill completely the gaps to be sealed but not to penetrate into fine structure portions such as the nozzle, and to be easily handleable. From such reasons, moisture-curing one-pack type silicone sealant is conventionally used for the sealing. This is because the silicone sealant has high ink resistance, high adhesiveness, moisture-curability, and possibility of giving desired viscosity and tack-free time.
One important problem involved in the ink jet head is prevention of formation of an air bubble. If an air bubble is formed in the ink flow path or the ink liquid chamber in the ink jet head, the energy for ejection is absorbed by the air bubble, making ink ejection instable or interrupting ink supply. The removal of the air bubble is conventionally practiced by sucking the ink by means of a recovery pump equipped in the ink jet apparatus. However, after the removal of the air bubble, the air bubble will again be formed gradually in the ink during standing of the head to result in the aforementioned inconvenience. Therefore, the recovery operation for the ink head needs to be practiced frequently. In recent years, the ink jet apparatus is required to be miniaturized, and therefore the ink-storing capacity of the ink tank tends to be made smaller and the ink absorption capacity of the waste ink absorbent also tends to be made smaller. Thus, it is an important technical problem to abate the recovery pump operation to the utmost for miniaturization of the ink jet apparatus.
After comprehensive investigation on the aforementioned air bubble formation, it was found by the inventors of the present invention that the principal cause of the bubble formation is penetration of gas through the silicone sealant, although other causes are involved such as looseness between the constituting members, the material of the constituting members, degree of air bubble removal depending on suction conditions with recovery pump.
The organosilicone compound conventionally used as the moisture-curing silicone sealant is assumed to have high gas permeability and allows formation of air bubble in the ink flow path, probably because the compound has large bond distance between the silicon and the carbon atom or other atom.
The inventors noticed the importance of the sealant, and investigated the sealant to replace the conventional moisture-curing one-pack type silicone sealant.
To solve the aforementioned problem of gas penetration, use of an organic high polymer was considered which has a high gas barrier property. General-purpose organic high polymers have lower gas permeability than the silicone type high polymers by a factor of 100. However, the organic high polymers themselves are not useful for the sealing material. Few organic high polymers are moisture-curable, or are not satisfactory in resistance to ink, adhesiveness to constituting members, and so forth.
Use of a moisture-curing one-pack type sealant is indispensable for sealing the gaps between the members of the ink jet head, which is brought into contact with ink, for stable and simple production of the heads. Since the ink jet head is constituted by various molded resin parts, the head cannot readily be sealed by pouring a thermoplastic resin or using a thermosetting resin. On the other hand, use of a two-pack type curing resin for the sealing of the head is not suitable for industrial production since the two curing components need to be mixed immediately before the use and have to be used within a prescribed time. The moisture-curing type resin penetrates into the gaps between the head-constructing parts by a capillary phenomenon and stops the penetration by forming meniscus at the portion other than the gap, and finally cures. Therefore, the sealant penetrates stably into the gaps to be sealed, but does not enter the portion where the penetration of the sealant is not desired, advantageously.
Such desirable properties cannot be achieved with two-pack type sealing materials, photosensitive sealing materials, or thermosetting type sealing materials.
On the other hand, cyanoacrylate and moisture-curing type urethane sealing materials are not suitable since such materials are insufficient in ink-resistance because of the hydrolyzable acrylic bonding or urethane bonding in the molecule.